As an air-conditioning apparatus, such as a multi-air-conditioning apparatus for a building, an air-conditioning apparatus has existed which implements a cooling and heating mixed operation by causing a refrigerant to circulate from an outdoor unit to a relay unit and causing a heat medium, such as water, to circulate from the relay unit to an indoor unit so that the conveyance power of the heat medium is reduced while the heat medium, such as water, is circulating in the indoor unit (see, for example, Patent Literature 1).
Furthermore, a circuit which injects liquid into the middle of a compressor from a high-pressure liquid pipe in a refrigeration cycle in order to reduce the discharge temperature of the compressor and an air-conditioning apparatus which is capable of controlling the discharge temperature to a set temperature, regardless of the operating state, have existed (see, for example, Patent Literature 2).
Furthermore, an air-conditioning apparatus exists which is capable of injecting a liquid refrigerant in a high-pressure state in a refrigeration cycle into a suction side of a compressor either in a cooling operation or a heating operation (see, for example Patent Literature 3).